1. Field of the Invention
The present invention relates to a method of acquiring an image representing a brain surface anatomy and a system for practicing the method.
2. Description of the Related Art
In a magnetic resonance (MR) phenomenon, an atomic nucleus having a magnetic moment and placed in a static field absorbs or emits an electromagnetic wave having a specific frequency by resonance. A resonance frequency (Lamor frequency) .nu..sub.0 of the atomic nucleus is represented by the following equation:
.nu..sub.0 =.gamma.H.sub.0 /2.pi. (1)
where .gamma. is the magnetogyric ratio unique to the type of atomic nucleus, and H.sub.0 is the strength of a static field.
An apparatus for diagnosing the inside of a subject by utilizing the MR phenomenon detects an electromagnetic wave generated inside the subject and processes the electromagnetic wave as an MR signal. A slice image of the subject which includes an atomic nucleus density, a longitudinal relaxation time T1, a lateral relaxation time T2, a flow, and a chemical shift can be noninvasively obtained. The MR signal can be obtained by exciting the entire subject placed in the static field. However, in practice, a predetermined portion of the subject is excited to obtain the MR signal due to structural limitations of the apparatus and clinical requirements.
In a surgical treatment for a disease within a cranium, it is very important to acquire an image representing an anatomy of a brain surface such as brain grooves or the like in order to grasp the position of a local cortical or subcortical disease portion. For this reason, images are acquired by MRI. For example, when a head coil having a shape for surrounding a head of a subject is used, images including subcortical information are obtained since an MR signal for the entire head is acquired. When a surface coil is used, many MR signals from the subcutaneous fat and the like of the surface layer are obtained by sensibility characteristics (highly sensible to signals from a portion near the coil) of the coil. Therefore, it is difficult to accurately grasp the position of a local cortical or subcortical disease portion in the head.
Strong demand therefore has arisen for an apparatus capable of acquiring a brain surface anatomy in order to accurately grasp the positions of disease portions located on the brain surface of the head of the subject.